The design problem

Sainsbury’s were committed to delivering a new 20,000sqft (gross sales) BREEAM assessed low carbon store intended as an exemplar within their portfolio. A number of headline objectives and opportunities were highlighted that would not only deliver the expectations of the town and county but would also aim at delivering a new benchmark for the Food Retailer and wider Construction industry. Some of the key directives to achieve this were:

To achieve a 30% reduction in operational energy and a reduction of 25% in operational carbon.

To measure embodied carbon footprint of the store and to reduce it by 20% against Sainsbury’s benchmark.

Provision for at least 20% renewable energy production on-site.

To achieve 40% reduction of potable against benchmark use.

Through recycling or other means to divert at least 90% of construction waste from landfill and maximise on site recycling facilities for ongoing operational waste from the store.

To maximise the landscape opportunity and make a strong contribution to the improvement of the local urban environment.

To minimise and eradicate as far as is practical all environmental pollution caused by the store in terms of surface water, GHG’s, noise and light.

The site

The building is located at the Gateway to Dartmouth to the west of the town on a steeply sloping site. As a result of the topography the building has been placed near to the southern boundary and is set into a sloping bank to present a low profile to Townstal Road, minimising its impact on views from the road and more distant viewpoints to the south. Therefore the store appears as a single storey structure when viewed from Townstal Road and 2 storey’s when viewed from Nelson Road or the new customer car park.

A newly constructed Devon hedge bank continues from the entrance and wraps around the North West corner where it runs to approximately 4 metres and adjoins a new hedgerow consisting of local native species namely Hawthorne, Hazel, Wayfaring tree and Privet which run along the entire northern boundary. The Devon hedge continues around the eastern edge of the site and is further reinforced with native structure planting and compliments an extensive landscaping scheme to help the building ‘blend in’ with its rural environment. Existing hedgerows have been extended and reinforced along the southern boundary towards the western edge of the site.

The architectural response

The rural nature of the existing site has influenced the appearance of the proposed building and the rural vernacular has been referenced in the design of the roof, walls and landscaping. The naturally undulating roof was designed to mimic a rolling Devon hillside and is finished with a metal standing seam roof, referencing agricultural barns. The solid walls have a natural and sustainable reference with Scandinavian pine (Thermowood) timber boarding and Limetec thin coat rough cast render. As juxtaposition to these natural elements the aluminium curtain walled façade facing west provided natural light to flood the sales floor and is protected by an overhanging roof to provide solar shading during the summer months.

A Glulam European whitewood spruce timber frame was chosen due to its reduction in embedded carbon. Within the sales floor itself the light finish of the timber beams and the spacing between the timber columns allow uninterrupted views of the store. The Terrazzo sales floor had a local aggregate added to it which made the floor appear lighter than normal, this coupled with the sun pipes in the roof letting natural light into the space provides a bright and clean environment for customers to experience.

Design strategies

Timber: A Glulam European whitewood spruce timber frame was chosen over steel due to its reduction in embedded carbon.

Rainwater conservation: 40% reduction of potable water against benchmark use. Rainwater harvesting and waterless urinals were used in order to help meet this requirement.

Daylighting: top lighting: 82 number 750mm dia Sunpipes were installed in the roof to reduce the amount of artificial lighting required to light the sales floor.

Solar controls and shading: The main glazed building facade faces West and is protected by the overhanging roof to provide solar shading to the sales floor during the summer months.

Biomass: A 90% efficient broag wood pellet boiler is installed to provide 100% of the total heating for the store which will save an estimated 164 tonnes of Carbon Per Annum. The pellets for the boiler are sourced locally.

On site wind power: 2 no. 21m high Quiet Revolution wind turbines are installed saving an estimated 8 tonnes of carbon per annum.

Lessons learned

The curved design of the roof, early decision to manufacture the structural frame from timber and the need to have a relatively clear floor space free from columns presented a challenge to the design team. The naturally curving glulam beams were engineered to allow a larger column spacing internally to maximise future flexibility. Careful consideration to the practicality of transporting large lengths of timber along Devon’s winding roads to the site from the factory in Austria was also factored into the design.

The building along the south elevation had to be treated as a boundary wall condition for fire protection. The construction of the external walls to enable the building to become ‘watertight’ early on in the programme meant that Kingspan Ecosafe cladding panels were used as a background for the applied timber cladding and limetec render. These panels had never been tested and certified when fixed to timber cladding rails. The design team were clear from the start that the appearance of the external walls of the building, when viewed internally, should all be uniform and should not be compromised by introducing cold rolled members to ensure compliance of this elevation; therefore the team liaised with Kingspan and the BRE who prepared a desktop evaluation to prove that the wall construction with oversized timber cladding rails provided the required 60 minutes fire resistance.